A new collection of plants, insects, fish and other fossils offers an unprecedented snapshot of Australia’s wetter, forest-dominated past.
McGraths Flat in New South Wales contains thousands of beautifully preserved specimens of flowering plants, ferns, spiders, insects and fish, vertebrate paleontologist Matthew McCurry and colleagues report Jan. 7 science progress.
Soft-tissue images of the fossils, captured by a scanning electron microscope, reveal them in stunning detail, from the sides of the compound eye of a crane fly to the mock midges trapped in a fish’s stomach.
Once upon a time, Australia was full of rainforests. During the Miocene epoch, about 23 million to 5 million years ago, the Earth underwent climatic disturbance. For Australia, that meant drought, with shrubs, grasses and deserts expanding into the lands that were once fertile. The McGraths Flat formed during that transition period, between 16 million and 11 million years ago. At the time, it was part of a temperate forest around a small lake, according to new analyzes of fossil pollen and leaves.
The researchers suggest that the fossils were embedded within minute layers of goethite, the mineral iron hydroxide that is probably acidic groundwater circulating through basalt rocks, causing iron seepage. When groundwater seeps into the lake, the iron oxidizes and turns into goethite particles. The tiny particles covered plants, insects, and other creatures in the water – probably while they were still alive – and later replaced some of the organisms’ internal structures.
“Until we studied these fossils, we hadn’t thought about looking for well-preserved fossils in this type of rock,” says McCurry, of the Australian Museum Research Institute in Sydney. At other fossil-rich sites known to preserve soft tissues, such as the Canadian Burgess Shale or the Chengjiang biota in China, the organisms tend to be covered with the kind of fine mud found on the sea floor (SN: 11/28/11; SN: 3/21/19). But, says McCurry, this site explains that goethite “has everything you need to create exceptionally well-preserved specimens.”